1. Field of the Invention
The invention relates to a process for forming a contact, and more particularly to a process for forming a contact in producing a MOS transistor such as DRAM, SRAM and Mask ROM and in producing bipolar devices and CCDS.
2. Description of the Related Art
In recent years, LSI devices have been further subminiaturized, as by contacts for N.sup.+ (or P.sup.+) diffused regions being reduced in thickness to 0.1-0.15 .mu.m. The thickness of interlayer films to be formed for such contacts largely varies depending on specific underlying patterns. Hence, in an etching process for the contact holes, the amount of Si erosion (which tends to occur at the N.sup.+ or P.sup.+ regions) is controlled by use of a contact mask corresponding to the depth of contacts.
FIG. 2 shows a conventional manufacturing method of a semiconductor device.
A LOCOS oxide film 11 is first provided on a substrate 10 of Si, on which are formed an electrode or a wiring layer 12 of polycide or the like and a spacer 13 adjoining thereto (FIG. 2(a)). A NSG film 14 of 1000-2000 .ANG. is deposited on the substrate 10, polycide 12 and spacer 13, followed by annealing (FIG. 2(b)).
A BPSG film 15 of 4000-6000 .ANG. is also deposited on the NSG film 14 (FIG. 2(c)).
A BPSG film 15 is flowed at 800.degree.-950.degree. C. over NSG film 14 to build a flat surface on the device (FIG. 2(d)).
The flattening process by the BPSG flow does not provide a relevant difference of thickness of the films at the contact forming part at which difference of the film thickness is actually over 5000 .ANG. at the opening portion h due to dispersion in density of BPSG previously deposited. This leads to such a problem that Si erosion is not controlled but occurs at the N.sup.+ and P.sup.+ regions upon dry etching process of the opening portion h in the sequential procedures.